The present disclosure relates generally to communication systems, and more particularly to methods and apparatuses for communicating using radiant energy signals in the presence of radio frequency energy.
The capabilities, features and functions of wireless communication devices, such as cellular radiotelephones, pagers and the like, have expanded tremendously and continue to grow. Within the devices themselves, for example, it is now possible to store and retain numerous names with associated phone numbers and addresses. It is also possible to keep an appointment calendar, task list and other personal organizer information within the memory of the wireless communication device. While the wireless communication device is typically designed to utilize one or more wireless communication standards for providing primary two-way voice and data communications via a communication network, to facilitate the exchange of data between devices, e.g., between other wireless communication devices, personal computers (PCs), personal digital assistants (PDAs), and the like, a secondary, low-power data transmitter and receiver may be provided.
Infrared (IR) communication technology provides a convenient form of low-power, limited range, wireless data transmission. Hence, it is not surprising that this technology has been adapted to wireless communication devices to allow these devices to communicate with other such devices and with IR capable PCs, PDAs and the like. For example, low cost, compact modules, such as the HSDL-3201 IrDA data transceiver available from Hewlett-Packard, are designed for adaptation to wireless communication devices and provide relatively fast data transfer using IR transmission and reception. These devices may provide a communication link from between 20-100 centimeters (cm), and data transmission rates up to 115.2 kilobits/second (kb/s).
A complication that arises from the inclusion of IR transceivers in radio frequency (RF) wireless communication devices relates to the electromagnetic fields produced by the wireless communication device. For example, a cellular radiotelephone may produce an electromagnetic field in close proximity to the antenna as high as 1 volt/meter. This field strength can effect electronic devices within a range of up to a meter. As noted, commercially available IR transceivers are typically designed to operate within about 20-30 cm, which is well within the relatively strong RF field created by the wireless communication device.
A problem arises if the electronic devices do not operate correctly in the presence of the large RF fields. While the wireless communication device is designed to operate within these fields, and therefore, is unlikely to have its operation effected by them, many peripheral devices may not be so tolerant. And, even where a device is designed with appropriate shielding and filtering to guard against anomalous circuit operation and to reject noise generated as a result of the field, if the field is strong enough, operation of the device may still be adversely effected. The end result is an end user that is dissatisfied with the performance of the wireless communication device and/or the peripheral device for exchanging data.
One reason why these devices may be affected by the RF field is found in the design of the peripheral device. For example, the conductive traces and wiring leads within the peripheral device act like antennas to the RF field thereby coupling the RF energy from the field into the transceiver circuit. Also, the IR module includes a receiver, and the receiver will necessarily include amplifiers and other non-linear devices. It is possible, in the presence of a strong enough RF field, that these devices will actually rectify the RF energy within the field generating a current wave. This current wave can easily overload the following circuit elements. Furthermore, the transimpedance amplifier typically found in IR receivers can convert the current wave to a noise voltage thereby reducing the signal-to-noise ratio significantly. Thus, there is a need for an apparatus and method for communicating in the presence of RF energy.